Synthetic paper sheet of chemically bonded synthetic polymer fibers and process of making the same



Jan. 20, 1959 J K. HUBBARD ETAL 2,869,973

SYNTHETIC PAPER SHEET OF CHEMICALLY BONDED SYNTHETIC POLYMER FIBERS ANDPROCESS OF MAKING THE SAME Filed Aug. 25, 1954 INVENTORS JAMES K.HUBBARD FRANKLIN H. KOONTZ M4. WWW

ATTORNEY United States Patent SYNTHETIC PAPER SHEET OF CHEMICALLY BONDEDSYNTHETIC POLYMER FIBERS AND PROCESS OF MAKING THE SAME James K.Hubbard, West Chester, and Franklin H.

Koontz, Marcus Hook, Pa., assignors to E. I. du Pont de Nernours &Company, Wilmington, DeL, a corporation of Delaware Application August25, 1954, Serial No. 452,022

14 Claims. (Cl. 8-1301) This invention relates to a novel article ofcommerce and to a process for its preparation. More particularly, it isconcerned with a paper-like pellicle of a mass of self-bonded,molecularly oriented fiber, produced from a linear synthetic polymerwherein recurring units are linked through amide nitrogen and a processfor its production.

By the expression a linear synthetic polymer wherein recurring units arelinked through amide nitrogen is meant a member of the class comprisingpolyamide, polyurethane, polyurea and polysulfonamide. The nitrogenlinkages between the recurring units may be represented as wherein andand R is hydrogen, lower alkyl and lower alkylene when the diamine has aring structure, such as in the case of piperazine.

The failure of synthetic fibers to replace cellulose to any appreciableextent in the past in the manufacture of paper-like structures, despitethe inherent desirable properties of the synthetic fibers such as highwet strength, toughness, chemical durability, excellent dimensionalstability and the like, is due largely to two factors, namely, theinability of such synthetic fibers to fibrilate, thus rendering themunsuitable for fabrication upon conventional commercial paper-makingequipment and also the inability of prior known methods to adequatelybond the reticulated mass without loss of desirable fiber propertiessuch'as molecular orientation. For instance it has been common inattempts to produce such structures to heat a ,batt of synthetic fibersunder pressure to fuse the matted fibers at points of intersection. Sucha product partakes almost completely of the physical properties of afilm of a similar synthetic polymer, the molecular orientation havingbeen largely randomized by the heat and necessary plastic flow. Polymerdegradation sometimes occurs. A similar effect is obtained when a battis bonded by partially dissolving it with a solvent and afterapplication of pressure, evaporating off the solvent. Solvent bonding isparticularly poor when applied to fibers and/ or filaments of syntheticcondensation polymers. Other attempts to form such a product haveemployed various bonding agents to join the crossed fibers in the mattedstructure. Such a product is limited in its properties by the chemicaland physical characteristics of the bonding agent itself and also theadhesive power of the bond for the fiber. Furthermore, when hightemperature is rev 2,869,973 Patented Jan. 20, 1959 2. quired to applythe bonding agent, molecular alignment of the fiber suffers.

It is an object of the present invention to provide a paper-likepellicle of a self-bonded, molecularly oriented fiber mass produced froma linear synthetic polymer wherein recurring units are linked throughamide nitrogen.

Another object is to provide a process for the preparation of such apaper-like pellicle adaptable to conventional paper-making equipment.

These and other objects will become apparent in the course of thefollowing specification and claims.

In accordance with the present invention a paper-like pellicle of a massof self-bonded, molecularly oriented fiber produced from a syntheticlinear polymer wherein recurring units are linked through amide nitrogenis formed by supplying a solution of join-inducing salt, to be describedhereinafter, to the surface of appropriate fibers and/or filaments priorto matting or in a matted form and heating to remove solvent. Theresulting paper- 'like pellicle is self-bonded, i. e., a true joining offibers and/or filaments at point of intersection is attained without thepresence of an added adhesive. Since the joining occurs at a relativelylow temperature, the fibers retain molecular alignment. Furthermore, theaction of the join inducing salt is a surface phenomenon concentrated atthe points of contact of the crossing fibers thereby not substantiallyaffecting the greater portion of the fiber structure. Pressure may beapplied during the joining operation to increase compactness of thefinal product. After formation, the pellicle may be washed free of thejoin-inducing salt. The product being unitary, self-bondedand'molecularly aligned, is both tough and flexible.

The invention will be more readily understood by reference to thedrawings.

Figure 1 is a photomicrograph of a fragmentary section of a batt ofmolecularly oriented fibers produced from a polyamide polymer.

Figure 2 is a photomicrograph of a fragmentary section of a paper-likepellicle produced from the mass of fiber of Figure 1 of the presentinvention.

In Figure l, a typical section of a batt of randomly disposedpolyhexamethylene adiparnide staple is shown. After treatment of thebatt in accordance with the present invention a join of the fibers attheir points of intersection occurs by virtue of self-bonding, i. e.,without benefit of an adhesive, as is shown in the photomicrograph ofFigure 2.

In general the mechanics of the process described herein are analagousto those of paper making. Thus the process is readily adaptable toconventional paper-making equipment, although not limited thereto. Inone embodiment a batt of fibers is formed on a moving screen. Since thefiber stock can be added from a liquid suspension, the Fourdriniermachine is convenient for this operation. The join-inducing salt can beadded to the mixer or showered upon the batt after its formation on theendless screen. Adequate heat and pressure for the join occurs withinthe felt-drying blanket at the dryer rolls. For the production of a lowporosity product, additional heat and pressure may be supplied bypassing the batt through a heated calendar roll. The salt may be removedby a water wash at the usual sizing station or the joined mass may bepassed through a wash tank. Manufacture may also be performed on thecylinder paper machine by similar modification.

The join inducing salt is a hydrate-forming salt of an inorganic acid,sufiiciently soluble in water to yield at least 10% and preferably 30%solutions, the aqueous concentrated solutions being capable ofdissolving the synthetic condensation polymer from which the pellicleride, ferric chloride, cadmium iodide, and the like.

is prepared at some temperature up to the boiling point or 7' of thesalt solution (for example from to 175 C., and 0 generally from 20 to 90C.). Solubility is readily determined by placing 0.1 gram of the finelydivided poly- 'mer in ml. of concentrated aqueous salt solution andstirring the mixture, with heating, if necessary, and ob- .servingwhether the polymer balls up to a coherent mass and/or passes intosolution. Soluble low molecular weight polymers tend to pass rapidlyinto solution, while soluble high molecular weight polymers absorb thesalt solution and coalesce before slowly passing into solution. Amongthe salts which meet the above definition are included ammoniumthiocyanate, lithium thiocyanate,

lithium iodide, lithium bromide, sodium thiocyanate, sodium iodide,-potassium thiocyanate, magnesium chloride, cupric chloride, calciumthiocyanate, calcium iodide, calcium bromide, zinc iodide, zinc bromide,zinc chlo- In general these salts are found among the water-solublethiocyanates, iodides, bromides, and chlorides of group I and II metalsof atomic numbers 3 to 48 or compatible mixtures of these salts. Thepreferred salts are the thiocyanates and chlorides. The preferredcations are ammonium, potassium, sodium, lithium, calcium, magnesium,zinc and ferric iron.

Among the specific polyamides included within the present invention arethose formed by the condensation polymerization of a dibasic acid or anamide-forming derivative thereof, such as idipic, sebacic, suberic,azelaic acids or the like, and adiamine such as piperazine, bisaminocyclohexane, ethylene, tetramethylene, pentamethyIene heXamethyIene,decamethylene, para-xylylene diamines or the like. Such materials mayalso be formed by other well knownmethods such as by polymerization ofamino acids or caprolactam. The fiber-forming polyurethanes are wellknown and may conveniently be formed by condensation polymerization of adiisocyanate with a glycol. glycol, propylene glycol, petaglycol,diethylene glycol and the diisocyanate derivatives of toluylene diamine,ethylenediamine, hexamethylenediamine and the like. As specificexemplifications of polyureas there may be mentioned the polymerizationproduct of carbonyl chloride and piperazine as well as alkylene diaminessuch as hexamethylene diamine and the like. The polysulfonamides may beprepared by polymerization of disulfonyl chlorides suchas metabenzenedisulfonyl chloride with piperazine, an alkylene diamine, such ashexamethylene diamine, and thelike. nitrogen linkages, i. e., a linkageof the formula:

Specific combinations include ethylene These polymers all contain amidepiperazine.

l. and R is hydrogen or lower alkyl or lower alkylene when the diaminehas a ring structure such as in the case of Funicular structures havingmolecular orientation, such as molecularly oriented fibers, filaments,staple and the like are produced from such polymers by methods wellestablished in the art.

While the join-inducing salt when in concentrated aqueous solution mustbe capable of dissolving the condensation polymer, it is applied to thefiber batt in a liquid carrier at a concentration, which under theconditions of application has little, or preferably no solvent actionupon the fiber. As the liquid carrier is evaporated, the capillaryforces at the points of fiber intersection tend to concentrate thejoin-inducing salt. Thus when the join is made by application of heatupon the substantially dry batt, the action of the salt is concentratedat the points of crossing and the major length of the fiber isunaffected.-

The following examples are cited to illustrate the invention; Theyare'not intendedto limit it in any manner.

EXAMPLE I Three grams of inch, 3 denier per filament staple ofpolyhexamethylene adipamide is suspended in a 6 liter aqueous solutioncontaining} grams of sodium carboxymethyl cellulose. The suspension isdispersed on at Rice- Barton Dyno pulper having two five-inch concavedisc's countercurrently stirring at 5000 revolutions per minute atopposite ends of a 5 gallon reservoir. Homogeneity is attained after 2minutes. Thereafter the aqueous dispersion is filtered over an 8" x 8"square of mesh screen, producing a randomly disposed mat of fibersreferred to hereinafter as a waterleaf. A vacuum of 350 mm. is employedto facilitate moisture removal and'to avert bubble entrainment. Thewaterleaf is gently showered with 20 liters of water to wash outresidual sodium carboxymethyl cellulose. 25 cc. of a 10% solu- .tion of.zinc bromide in water is showered upon the waterleaf. It is thereafterdried at C., pressed under a pressure of 200 p. s. i. at 160 C. for aperiod of 30 seconds, washed with 3 liters of waterto remove zincbromide and air dried. The resulting paper-like pellicle is self-bonded,has a tensile strength of 32 pounds per inch, a burst strength of 67pounds per square inch and a tear strength of 1056 grams. All of thesetests, as well as those reported hereinafter are made by the standardmethods reported in TAPPI Standards. A similarly prefi pared waterleafupon which bonding-is attempted under -AIT the same conditions, butwithout benefit of the join-in- R duclng zinc bromide salt, has atensile, strengthvof 0.2 wherein I 55 pound per inch, a burst strengthof 12.8 pounds per Elli square inch and a tear strength of 200 grams. II Table I- below is a summary of various other polyis hexarnethyleneadlparnide fiber pellicle preparations i1-.

fi lustratmg' modifications of the process described in Ex- C so ampleI. j

Table I Example Salt Solvent Cone. Temp. Press. Time Press Bond 7(Percent) V( O.) (lbs/in?) (see) Cond. i v

2- ZnBrz 1120 3.0 160 200 30 3 ZuClz E'IOH 10.0 50 30 4- ZHCIR ETOH 2. 5185 200 30 5- ZllClfl H20 10.0 200 30 6. 09.012 11 0. 10. 0, 200- 200 so7 CaBrz H20- .590 200 .30 8- Ca(CNS)a H2O, 5.0: 1160 200 30 9- MgC H2O10.0 160 200 30 10 Na(CNS) H20 10.0 .160 200 '30 11 011012 H20 10. 0.160 200 30 g p ge E%%H 10.0 .100, 200 30 F 1 r 2 5.0 160, 200 30 rvoood. 14 Mg(CNS )2 H10 'i- ".160 200 I -30 Dry.-." -VZGOodf 5 Themechanical properties of the pellicles of Table I are reported in TableII.

Table II Tensile Elonga- Burst Tear Exam. Strength, tion Strength,Strength,

lbs/in. p. s. i. grams EXAMPLE.

A /2 inch, 3 denier per filament staple of a copolymer of 2,5dimethylpiperazine, with a mixture of 65% terephthaloyl chloride and 35%ethylene bischloroformate is formed by the process described in Example12 of copending U. S. application No. 359,975, filed June 5, 1953, inthe name of Langsdorf and Wittbecker. Three grams of this staple is usedto form a pellicle following the technique of Example 1 of the presentapplication, employing calcium thiocyanate as the join-inducing salt asa 2.5% aqueous solution. The batt is pressed at 160 C. under 200 poundsper square inch for 30 seconds. The product is strong, soft andflexible. It has a burst strength of. 105 pounds per square inch.

EXAMPLE 16 EXAMPLE 17 A /2 inch, 3 denier per filament staple ofpolyamide is formed from a polymer produced by the polymerization ofcaprolactam. Substitution of this staple in the process of Example 15yields a product having a burst strength of 150 pounds per square inchand a tear strength of 256 grams.

EXAMPLE, 1:;

Six grams of inch, 1 denier per filament staple formed frompolyhexamethyleneadipamide is suspended in six liters of watercontaining 30 grams of carboxymethylcellulose (as thickener). A sheet offibers six inches square is formed. This leaf is then dipped in anaqueous solution containing by weight calcium chloride. Excess liquid iswrung from the leaf. It is pressed wet for seconds under 200 pounds persquare inch at 170 C. A dry, pliable film results, having a burststrength of 365 pounds per square inch, a tear strength of 1520 gramsand a tensile strength of 16 pounds per square inch.

The following example illustrates the formation of a continuous sheet ona Fourdrinier machine.

EXAMPLE 19 A staple feed is prepared by beating an aqueous suspension ofinch, 3 denier per filament staple produced frompolyhexamethyleneadipamide in a tugboat type beater for 15 minutes. Thestaple length is thereby reduced to an average of A inch. The suspendingliquid also contains 0.2% by weight based on the solution of sodiumlauryl sulfate (as a wetting agent) and 4% by weight calcium thiocyanateas a join-inducing salt. The suspension is fed to a small Fourdriniermachine (Franklin Institute, Philadelphia, Pa.) to produce a well-formedsheet. The machine has an 8 inch screen and is run at 6 feet per minute.As the sheet leaves the screen a squeeze roll removes excess liquid. Itprogresses through the drying felt over electrically heated rollsregulated at about C. The product is run through a water bath to removethe salt. It is soft, pliable and strong.

The method employed in forming the batt is not criti cal. It is notnecessary that the molecularly oriented fibers be suspendedin a liquidand beaten prior to batt formation since adherence among the fibers doesnot depend on fibrillation as is the case in cellulose papermanufacture. However, to attain uniform distribution it is convenient tosuspend a known weight of fibers or the like in a measured quantity ofliquid and agitate. Machines used in paper-making such as the Hollanderbeater, the Tugboat pulper, jordans and the like are all suitable. Toassist dispersion the Viscosity of the liquid may be raised. This may beaccomplished -by supplying an additive to water such as sodiumcarboxymethyl cellulose, partially hydrolyzed polyvinyl acetate (such asElvanol 72-51 manufactured by E. I. du Pont de Nemours & C0. ofWilmington, Delaware) the condensation product of ethanolamine withmixed long chain acids (such as Ninol 2012A, manufactured by Ninol Lab-Oratories of Chicago, Illinois), or the like, or by employing a highviscosity liquid such as glycerine, ethylene glycol, t-butyl alcohol orthe like. The optimum viscosity will vary with the type of mixing orbeating, the fiber denier, and similar factors. In choosing thesuspending media and thickener, therefore, care must be exercised toavoid substances which cannot be subsequently removed from the formedbatt with case since certai foreign substances such as for instancesodium carboxymethyl cellulose, even in minute concentrations, have beenfound to interfere with the formation of the join. In ibatt formationfrom a liquid suspension the use of staple having a length below about 1inch with a denier per filament within the range of from about to about6 is preferred. However these values may vary. Fibers of mixed lengthand denier are suitable. Fibers as short as $1 inch are satisfactory.Instead of laying the batt from liquid suspension, staple, fiber orfilament in Wet or dry condition may be blown or dopped upon a surface,or a continuous filament may be crossed lapped on a surface. Thefunicular structure may be crimped or uncrimped and of circular orirregular cross section.

The joindnducing salt may be applied to the funicular feed at any stageprior to the joining step. It is sometimes convenient to add it to theheater in which the batt-forming fibers are suspended. When it isdesirable to wash the batt after its formation, the salt may be addedafter the wash step. As previously described, the salt containingsolution applied to the batt or leaf is sufficiently dilute to avoid anysubstantial degradation and/or solution of the fiber structure. Themaximum concentration will vary according to the salt employed and theconditions, under which it is applied. In general a salt solutionsuflicient to. deposit at least about 10% by weight of salt based on thefabric Weight is desirable. A batt wherein salt constitutes by weight offrom about 20%. to about 30% is preferred.

The join step is generally accomplished by exposing the batt of fiberbearing the join-inducing salt to elevated temperature. The optimumtemperature will vary with the salt used, the amount of salt employed,the pressure upon the batt and the period of exposure. For a contactperiod of about thirty seconds a temperature within the range of fromabout 90 to about C. is usually adequate. While longer heating periodswhen operating within this temperature range may be employed withoutdeleterious efiects, short periods of three minutes or less arepreferred to facilitate commercial operations.

Temperatures sufficientljtp induce molecular randomlzation cause aweakening of the product and loss of flexibility. For the production ofa high strength, hard surface paper-like pellicle, a pressure within arange of from about 50 to about 200 pounds per square inch is usuallyemployed. A lower pressure to 'lbs)"produces a'bulkier product of softersurface.

The batt containing salt can be exposed to elevated temperature,preferably in a press as previously discussed, either in the moist ordry condition (i. c. after After the join is complete, the join-inducingsalt is washed from the self-bonded coherent mass. The product is atough, flexible, coherent paper-like pellicle. It is useful in themaking of paper money, as a filter media, as a non-woven fabric,- in themanufacture of reinforced plastic, as body armor, condenser paper, inhigh frequency electronic circuits, printed electrical circuits,stencils, permanent ledger, wall-paper and the like. While the inventionhas been exemplified in the production of flat structures, it is obviousthat shaped articles may be similarly formed by depositing the batt orleaf over a form and thereafter applying the necessary heat andpressure. Thus seamless cones, bags, apparel and the like may be made.

A fold endurance rating of about 52,000 is observed when the pellicle ofthe present invention is tested on an M. I. T. Folding Endurance Tester(Manfactured by Tinius Olsen Testing Machine Company of Willow Grove,Pennsylvania). This compares with a rating of about 1200 for a highgrade of kraft paper.

The following example is cited to illustrate utility.

EXAMPLE The pellicle produced in accordance with the directions ofExample 1 is folded into conical shape and employed to remove suspendedsolids from a 50% aqueous sodium hydroxide solution. Filtration israpid. No deleterious effect upon the folded pellicle is observed.

In summary the process of the present invention comprises heating to atemperature within a range of from about 90 C. to about 170 C. a batt ofa molecularly oriented fiber produced from a linear, synthetic polymerwherein recurring units are linked through amide nitrogen, the said battbearing at the points of fiber intersection a join-inducing salt aspreviously defined, which salt is originally applied to the said fiberat a concentration at which it is substantially innocuous to the said'fiber. The product may be conveniently defined as a paper-like pellicleof a mass of self-bonded, molecularly oriented fiber produced from alinear, synthetic polymer wherein recurring units are linked throughamide nitrogen, the said fiber bridged between points of fiberintersection possessing substantially its as-formed characteristics.

Many equivalent modifications within the inventive concept will beapparent to those skilled in the art from a reading of the foregoingdescription without a departure from the inventive concept.

What is claimed is:

1. A synthetic paper sheet composed of a batt consisting essentially ofa mass of reticulated molecularly oriented fiber, the said fiber beingcomposed of a fiberforming linear, synthetic polymer wherein recurringunits are linked through amide nitrogen to provide a recurring linkagefrom the class consisting of a polyamide, a polyurethane, a polyurea anda polysulfonamide, the said recurring linkage being an integral part ofthe polymer chain, the said fibers being self-bonded only at the pointswhere the fibers intersect each other, the said self-bond having beenaccomplished by a joininducing salt, those portions of the fibersbetween the points of fiber intersection po sessing nt a y the 8 samephysical and chemical characteristics as they possessed prior to theformationeof the bonds.

2. A process of making a synthetic paper sheet which comprises applying,to a batt of reticulated molecularly oriented fiber, the said fiberbeing composed of fiberforming linear, synthetic polymer whereinrecurring units are linked through amide nitrogen, to provide a polymerfrom the class consisting of a polyamide,'a polyurethane,

a polyurea and a polysulfonamide, the said recurring amide nitrogenbeing an integral part of the polymer chain, a solution consistingessentially ofa join-inducing salt for said fibers, the said salt beinga hydrate-forming salt of an inorganic acid sufficiently soluble inwaterto yield at least 10% solutions, the said solution being ini-'tially at a concentration sufficiently dilute to avoid substantiallyaltering the'physical and chemical properties of the fiber structure,heating the said batt bearing the said dilute salt solution until thesalt solution becomes concentrated and located substantially only at thepoints of fiber intersection, and the fibers are self-bonded to eachother at their points of intersection, those portions of the fibersbetween the points of fiber intersection possessing substantially thesame physical and chemical characteristics as they possessed prior tothe formation of the bonds, the said heating occurring over a period ofat least about 30 seconds and at a temperature within a range of fromabout C. to about C.

3. The process of claim 2 wherein a pressure of at least aboutSO poundsper square inch is applied to the batt during the period of heating.

4. The article of claim 1, wherein the polymer is a polyamide.

5. The article of claim 4 wherein the polymer is hexamethyleneadipamide.

6. The article of claim 1 wherein the polymer. is a polyurethane.

7. The article of claim 1 wherein the polymer is a polyurea.

8. The article of claim 1 wherein the polymer is a polysulfonamide.

9. The process of claim 2 wherein the solution of the saidhydrate-forming salt is applied to the fiber prior to batt formation.

10. The process of claim 2 wherein the solution of the saidhydrate-forming salt is applied to the batt after batt formation.

11. The process of claim 2 wherein the heating is performed with thebatt under a pressure of from about 50 to about 200 pounds per squareinch.

12. The process of claim 11 wherein the heating under pressure isapplied to the wet batt.

13. The process of claim 11 wherein the heating under pressure isapplied to the batt after removal of moisture by evaporation.

14. The process of claim 2 wherein the said hydrateforming salt is awater-soluble salt of a'metal of the first two groups of the periodicsystem having atomic numbers from 3 to 48.

References Cited in the file of this patent UNITED STATES PATENTS1,719,173 Dreyfus July 2, 1929 2,030,625 Ellis Feb. 11, 1936 2,198,269Linzell et al Apr. 23, 1940 2,357,392 Francis Sept. 5, 1944 2,357,962Leeman et al. Sept. 12, 1944 2,600,504 Leeds et al June 17, 19522,622,960 Woods Dec. 23, 1952 2,626,214 Osborne Jan. 30, 1953 2,692,183Ericks Oct. 19, 1954 2,730,479 Gibson Jan. 10, 1956 2,734,001Mecklenburgh Feb. 7, 1956 a FOREIGN PATENTS 674,577 Great Britain June25, 1952

1. A SYNTHETIC PAPER SHEET COMPOSED OF A BATT CONSISTING ESSENTIALLY OFA MASS OF RETICULATED MOLECULARLY ORIENTED FIBER, THE SAID FIBER BEINGCOMPOSED OF A FIBER FORMING LINEAR, SYNTHETIC POLYMER WHEN RECURRINGUNITS ARE LINKED THROUGH AMIDE NITROGEN TO PROVIDE A RECURRING LINKAGEFROM THE CLASS CONSISTING OF A POLYAMIDE, A POLYURETHANE, A POLYUREA ANDA POLYSULFONAMIDE, THE SAID RECURRING LINKAGE BEING AN INTEGRAL PART OFTHE POLYMER CHAIN, THE SAID FIBERS BEING SELF-BONDED ONLY AT THE POINTSWHERE THE FIBERS INTERSECT EACH OTHER, THE SAID SELF-BOND HAVING BEENACCOMPLISHED BY A JOININDUCING SALT, THOSE PORTIONS OF THE FIBERSBETWEEN THE POINTS OF FIBER INTERSECTION POSSESSING SUBSTANTIALLY THESAME PHYSICAL AND CHEMICAL CHARACTERISTICS AS THEY POSSESSED PRIOR TOTHE FORMATION OF THE BONDS.
 2. A PROCESS OF MAKING A SYNTHETIC PAPERSHEET WHICH COMPRISES APPLYING, TO A BATT OF RETICULATED MOLECULARLYORIENTED FIBER, THE SAID FIBER BEING COMPOSED OF FIBERFORMING LINEAR,SYNTHETIC POLYMER WHEREIN RECURRING UNITS ARE LINKED THROUGH AMIDENITROGEN, TO PROVIDE A POLYMER FROM THE CLASS CONSISTING OF A POLYAMIDE,THE SAID RECURRING A POLYUREA AND A POLYSULFONAMIDE, THE SAID RECURRINGAMIDE NITROGEN BEING AN INTEGRAL PART OF THE POLYMER CHAIN, A SOLUTIONCONSISTING ESSENTIALLY OF A JOIN-INDUCING SALT FOR SAID FIBERS, THE SAIDSALT BEING A HYDRATE-FORMING SALT OF AN INORGANIC ACID SUFFICIENTLYSOLUBLE IN WATER TO YIELD AT LEAST 10% SOLUTIONS, THE SAID SOLUTIONBEING INITIALLY AT A CONCENTRATION SUFFICIENTLY DILUTE TO AVOIDSUBSTANTIALLY ALTERING THE PHYSICAL AND CHEMICAL PROPERTIES OF THE FIBERSTRUCTURE, HEATING THE SAID BATT BEARING THE SAID DILUTE SALT SOLUTIONUNTIL THE SALT SOLUTION BECOMES CONCENTRATED AND LOCATED SUBSTANTIALLYONLY AT THE POINTS OF FIBER INTERSECTION, AND THE FIBERS ARE SELF-BONDEDTO EACH OTHER AT THEIR POINTS OF INTERSECTION, THOSE PORTIONS OF THEFIBERS BETWEEN THE POINTS OF FIBER INTERSECTION POSSESSING SUBSTANTIALLYTHE SAME PHYSICAL AND CHEMICAL CHARACTERISTICS AS THEY POSSESSED PRIORTO THE FORMATION OF THE BONDS, THE SAID HEATING OCCURING OVER A PERIODOF AT LEAST ABOUT 30 SECONDS AND AT A TEMPERATURE WITHIN A RANGE OF FROMABOUT 90*C. TO ABOUT 170*C.